This invention relates generally to improved centrifugal pumps. More particularly, but not by way of limitation, this invention relates to method and apparatus for increasing the efficiency of centrifugal pumps when used at less than design capacity.
In multistage centrifugal pumps, pumping less than the capacity of liquid therethrough may result in internal recirculation within the pump which substantially lowers the efficiency of the pump and may, in some instances, be so severe as to cause damage or destruction to the pump. It has been found that such internal recirculation is predominant in the first stage of multistage pumps.
In the past, when pumps were to be used to deliver less liquid than their design capacity, great care has been taken to make certain that adequate liquid has been pumped thereby to maintain the throughput of the pump above the design value of the internal recirculation problem. To accomplish this, multistage centrifugal pumps in the past have had a bypass arrangement at the discharge permitting fluid in excess of the demand value to either be recirculated to the pump inlet or disposed of in some other means. In any event, the energy lost by having to pump the entire quantity through the entire pump before bypassing has had a severe effect on the efficiency of multistage centrifugal pumps when operating at less than design capacity.
In the applications of multistage centrifugal pumps such as when used as boiler feed pumps, it is necessary that the pumps be designed to handle the maximum volume of liquid that may be required by the system operating at peak load. Accordingly, such pumps will frequently be operated at less than capacity when the demand is not at the peak load.
An object of this invention is to provide improved methods and apparatus for increasing the efficiency of multistage centrifugal pumps when they are operating at less than the design capacity.